Quartz crystal microbalance technique methods

A variety of surface-sensitive spectroscopic and microscopic methods were critical in the investigation of these systems. In the work by Advincula et al, the composition, thickness, physical and thermal properties, and morphology of the tethered polymer brushes were carefully analyzed [72]. A variety of surface-sensitive techniques such as ellipsometry, contact angle measurements, AFM, quartz crystal microbalance (QCM), FT-IR grazing incidence... 

Variations on the vertical dipping technique have been utilized to construct films containing divalent metal ions. For example, the quartz crystal microbalance (QCM) has been used to evaluate the horizontal lifting method of CdSt LB Film construction (26). In this method, the QCM quartz plate was touched to monolayers compressed on a subphase and lifted horizontally. Y-type transfer (transfer ratio of 1) was demonstrated with two centrosymmetric monolayers deposited for each cycle. A combination of the vertical and horizontal dipping techniques has been utilized to prepare multilayer films from an amphiphilic porphyrin compound (27). 

Fig. 6.97. Some techniques used in the study of isotherms (a) Electrochemical quartz crystal microbalance mass change (AW) vs. quantity of electricity (AG) [Au, 0.1 M HCI04 (a), and 0.05 MH2S04 ( )] and anion coverage vs. electrode potential [poly-Au (open symbols), and Au(111) (dark symbols) HS04 (circles) and CI04 (triangles)]. Reprinted from H. Uchida, N. Ideda, and M. Watanabe, J. Electroanal. Chem. 42 , copyright 1997, Figs. 3 and 5, with permission of Elsevier Science.) (b) Specular reflection method reflectivity change vs. potential [Au, HCI04 with Nal (b) and (c) 0...

Our approach to this problem involves a detailed mechanistic study of model systems, in order to identify the (electro)chemical parameters and the physicochemical processes of importance. This approach takes advantage of one of the major developments in electrochemical science over the last two decades, namely the simultaneous application of /ton-electrochemical techniques to study interfaces maintained under electrochemical control [3-5]. In general terms, spectroscopic methods have provided insight into the detailed structure at a variety of levels, from atomic to morphological, of surface-bound films. Other in situ methods, such as ellipsometry [6], neutron reflectivity [7] and the electrochemical quartz crystal microbalance (EQCM) [8-10], have provided insight into the overall penetration of mobile species (ions, solvent and other small molecules) into polymer films, along with spatial distributions of these mobile species and of the polymer itself. Of these techniques, the one upon which we rely directly here is the EQCM, whose operation and capability we now briefly review. 

This phenomenon has been studied by different combined electrochemical techniques such as -> spectroelec-trochemistry, radioactive -> tracer method, -> electrochemical quartz crystal microbalance, conductivity etc. by varying the experimental parameters, e.g., film thickness, the composition and concentration of the electrolyte solutions, the wait-time at different waiting potentials, and temperature [iii-x]. Several interpretations have been developed beside the ESCR model. The linear dependence of the anodic peak potential on the logarithm of the time of cathodic electrolysis (wait-time) -when the polymer in its reduced state is an insulator -has been interpreted by using the concept of electric percolation [ix]. Other effects have also been taken into account such as incomplete reduction [vii], slow sorp-tion/desorption of ions and solvent molecules [iii-vi], variation of the equilibrium constants of -+polarons and - bipolarons [viii], dimerization [xi], heterogeneous effects [xii], etc. 

Through the combination of SPR with a - poten-tiostat, SPR can be measured in-situ during an electrochemical experiment (electrochemical surface plasmon resonace, ESPR). Respective setups are nowadays commercially available. Voltammetric methods, coupled to SPR, are advantageously utilized for investigations of - conducting polymers, thin film formation under influence of electric fields or potential variation, as well as - electropolymerization, or for development of -> biosensors and - modified electrodes. Further in-situ techniques, successfully used with SPR, include electrochemical - impedance measurements and -+ electrochemical quartz crystal microbalance. 

We will first describe briefly the main experimental techniques coupled with electrochemical methods Infrared Reflectance Spectroscopy (IRS), Electrochemical Quartz Crystal Microbalance (EQCM), Differential Electrochemical Mass Spectrometry (DEMS), Chemical Radiotracers and High Performance Liquid Chromatography (HPLC). 

In the gravimetric method, the adsorbent (usually in the form of powder) is placed into a bulb, which is mounted on a sensitive balance and the bulb is then evacuated. Next, the weight increase of the adsorbent solid as a function of the absorptive gas pressure is monitored at constant temperature. More recently, the quartz crystal microbalance (QCM) technique has been applied this is very sensitive to mass increases. Quartz is a piezoelectric material and the thin crystal can be excited to oscillate in a traverse shear mode at its resonance frequency when a.c. voltage is applied across the metal (usually gold) electrodes, which are layered on two faces of the crystal. When the mass on the crystal increases upon adsorption, its resonance frequency decreases. The increase in the mass is calculated from the reduction in resonance frequency. On the other hand, adsorption on single flat surfaces can also be measured by ellipsometry, which measures the film thickness of transparent films optically using the difference between light reflection from bare and adsorbed surfaces. 

The use of the quartz crystal microbalance in monitoring resist dissolution rates was first reported in 1985 by W.D. Hinsberg et al. This technique is based on the equation that G. Sauerbrey developed in 1959 as a method for correlating changes in the oscillation frequency of a piezoelectric crystal with the mass... 

In this chapter the synthetic aspects of the earlier mentioned [M(bipy)2 (PVPjnCl]" polymers (where M = Os,Ru) are discussed. The main part of the chapter is devoted to the effect of electrolyte and polymer loading on the electrochemistry observed at electrodes modified with these materials. Interaction between the polymer layer and the electrolyte is investigated using electrochemical techniques such as cyclic voltammetry, potential step methods, and the electrochemical quartz crystal microbalance. Attention is also paid to mediation reactions using such modified electrodes. Finally, the implications of these observations for analytical applications of these materials are discussed. 

The application of combinations of electrochemical methods with non-electro-chemical techniques, especially spectroelectrochemistiy (UV-VIS, FITR, ESR), the electrochemical quartz crystal microbalance (EQCM), radiotracer methods, probe beam deflection (PBD), various microscopies (STM, AFM, SECM), ellipsometiy, and in situ conductivity measurements, has enhanced our understanding of the nature of charge transport and charge transfer processes, stmcture-property relationships, and the mechanisms of chemical transformations that occur during charg-ing/discharging processes. 

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